Hammer for forming bulges in an array of compliant pin blanks

ABSTRACT

A hammer for forming bulges in an array of compliant pin blanks by compressive deformation to thereby attach the array of pin blanks to a printed circuit board is provided. Each of the compliant pin blanks has a substrate engaging portion and a compliant section spaced from the substrate engaging portion projecting from the printed circuit board. The compliant section of each pin blank defines at least one protrusion extending outwardly farther than the remaining portions of the compliant section of the pin blank. The circuit board has a plurality of holes receiving the pin blanks. A hammer is provided which has a body defining a substrate facing surface for facing the printed circuit board and defining a plurality of holes extending from the substrate facing surface for receiving the compliant sections of the pin blanks. The holes in the substrate facing surface have a bulge cavity larger than the cross-section of the portion of the pin receiving blank therein. The compressive stress of the pin blanks will cause the blanks to be formed in the bulge cavities.

This is a divisional of application Ser. No. 08/457,413, filed on Jun.1, 1995, now U.S. Pat. No. 5,715,595.

BACKGROUND OF THE INVENTION

The present invention relates to a novel pinned module and a method formaking the same.

In the manufacture of printed circuit boards and similar electricaldevices, it is desirable to make connections to the device as quicklyand easily as possible. One technique for making this connection is toemploy pins which are mechanically and sometimes electrically connectedto the device.

Many techniques are known for affixing electrical connection pins tocircuit boards and the like devices. One well known way is to providethe circuit board or device with an opening and to provide the pin witha compliant section having a size compatible with the opening such thatwhen the compliant section of the pin is inserted into the opening, itcoacts with the walls of the opening to maintain the pin affixed to thedevice or board. See U.S. Pat. No. 4,969,259, the disclosure of which isincorporated herein by reference. For convenience, this technique ofaffixing a pin to a substrate using a compliant section of the pin tointeract with the walls of an opening in the substrate shall be referredto hereinafter as "compliant pin connection."

Another well known method for connecting pins to circuit boards and thelike devices uses non-compliant pins. In this technique, a pin blank isinserted into a hole in the board or other device and the blank issubjected to compression along its longitudinal axis. As a result, theportions of the pin blank adjacent the two sides or surfaces of theboard deform through compressive stress to form bulges which securelylock the pin in place. For convenience, techniques for affixing pins inthis manner will be referred to hereinafter as "compressive deformationconnection."

In the design of complicated electronic components, it is not uncommonto arrange circuit boards and other like devices in stacked relationwith numerous electrical connections being made between the differentboards. Typically this is done by providing a first circuit board withpins of either the compliant or non-compliant types, moving a secondcircuit board into position so that the pins projecting from the firstcircuit board engage corresponding positions in the second circuit boardand then soldering the pins to the second circuit board to lock them inplace.

Although this procedure works well, it is disadvantageous because itemploys soldering operations, which are inherently time consuming, messyand expensive.

In order to overcome this disadvantage, it has been proposed to affixstacked circuit boards together by using electrical connection pins inwhich both boards are secured to the same pin by compliant pinconnection. See, for example, U.S. Pat. No. 4,446,505 and U.S. Pat. No.4,889,496, the disclosures of which are incorporated herein byreference. However, in these cases, either the mechanical/electricalconnection made with at least some of the pins in one or both boards isnot as good as desired or the procedures are complicated and expensivedue to the use of pin blanks of esoteric structure, special mechanicalmanipulations, or both.

Accordingly, it is an object of the present invention to provide a noveltechnique for forming electrical connections between two or more stackedprinted circuit boards by a simple and straightforward manner whichprovides excellent electrical/mechanical connection for all connections.

In addition, it is a further object of the present invention to providea novel circuit board or module for use in this technique.

A still further object of this invention is to provide a completedassembly of two or more stacked printed circuit boards or devices whichis made using this module.

In addition, it is a still further object of the present invention toprovide a method of affixing pin blanks to electrical substrates inorder to make the modules of the present invention.

Moreover, it is a still another object of this invention to provide anovel hammer or anvil for use in affixing pin blanks to substrates inaccordance with this method.

SUMMARY OF THE INVENTION

These and other objects are accomplished by the present invention inaccordance with which an electrical connection pin blank having at leastone compliant section is affixed to a first circuit board by compressivedeformation in such a way that the compliant section of the pin blankprojects outwardly from the surface of the first circuit board. The endof the pin projecting from the first circuit board is then inserted intoa corresponding opening in a second circuit board and the two boardsbrought together until the second circuit board is firmly affixed to thecomplaint section of the pin by compliant pin connection.

By this means, both the first and the second circuit boards are securelyconnected together, both mechanically and electrically, even when manypins are involved. Moreover, because soldering is avoided the attendantdisadvantages of soldering are also avoided. Furthermore, because thepin blanks employed are of conventional structure, and also because onlysimply mechanical movements are needed for each formation step, themanufacturing method is simple, easy and inexpensive to carry out.

In accordance with a further aspect of the invention, a novel hammer foraffixing pin blanks to a substrate by compressive deformation isprovided, the hammer defining holes for receiving the projecting ends ofa plurality of pin blanks, these projecting ends including compliant pinsections, the holes in the hammer being so shaped that they can receivethe projecting ends of the pin blanks including their compliantsections. By this means attachment of pins to a first circuit board bycompressive deformation can be easily accomplished, even though the pinsinclude compliant sections that would prevent them from being used inordinary hammers.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is more thoroughly illustrated in the followingdrawings wherein:

FIG. 1 is an exploded schematic view, in cross section, illustrating howa pin blank is affixed to a first circuit board by compressivedeformation in accordance with the present invention, with the parts andthe hammers used for this forming process being in a retracted position;and

FIG. 2 is a view similar to FIG. 1 showing the hammers in a closedposition with the pin being received in and affixed to the first circuitboard; and

FIG. 3 is an isometric view illustrating the module produced by thetechnique illustrated in FIGS. 1 and 2; and

FIG. 4 is another exploded schematic view illustrating how the module ofFIG. 3 is affixed to a second circuit board by compliant pin connection;and

FIG. 5 is a schematic view similar to FIG. 4 showing the parts of theforming machine in a closed position to form an assembly in accordancewith the present invention; and

FIG. 6 is a partial isometric view illustrating the completed assemblyproduced by the process illustrated in FIGS. 4 and 5; and

FIG. 7 is a view similar to FIG. 1 but shown in exploded isometric formfor illustrating the details of the hammer of the present invention usedto affix the pin blank to the first circuit board; and

FIG. 8 is an isometric view similar to FIG. 3 but showing anotherembodiment of the present invention; and

FIG. 9 is an isometric view illustrating a three-layered stackedassembly.

DETAILED DESCRIPTION

Referring to FIGS. 1 to 3, an electrical module generally indicated at10 (FIG. 3) is formed from a substrate 12 and a pin blank 14. In theembodiment shown, substrate 12 is a printed circuit board and iscomposed of a dielectric material such as ceramic, fiberglass-reinforcedepoxy such as FR4, etc., which contains one or more electricallyconductive paths (not shown) therein. Substrate 12 defines one or moreholes 16 therein which pass all the way through the substrate from afirst surface 18 thereof to a second surface 20 thereof. In theembodiment shown, hole 16 is a plated-through-hole, meaning that thesurfaces of hole 16 carry a coating of an electrically conductivematerial 22 which extends all the way through the hole from firstsurface 18 of the substrate to second surface 20 and extends outwardlyfrom the center of the hole by a small distance on these surfaces toform pads 23 as shown in FIG. 1. In the particular embodiment shown, theelectrically conductive material 22 of the plated-through-hole iselectrically connected to an electrically conductive path (not shown) inthe substrate.

As further shown in FIG. 1, pin blank 14 comprises a generally elongatedmember which defines a first end 24 and a second end 26. The body of pinblank 14 near first end 24 defines a substrate-engaging section 28 and,in a location spaced from substrate-engaging section 28, a firstcompliant section generally indicated at 30.

In the particular embodiment shown, first compliant section 30 includesprotrusions 32, which are formed by swaging and which extend outwardlyfrom the center line of pin blank 14 by a distance greater than theradius of the pin blank in the remainder of the pin blank body. Asdiscussed more fully below, the shape and size of protrusions 32 areselected so that these protrusions will cooperate with the walls ofopenings in a second circuit board to which the module 10 is to beattached.

In order to form the module of FIG. 3, pin blank 14 is arranged toregister with hole 16 in printed circuit board 12. In addition, printedcircuit board 12 and pin blank 14 are also arranged to register with apin blank receiving hole 34 in a lower hammer 36 as well as a bulgecavity 38 in an upper hammer 40, these hammers being part of a machine(not shown) for attaching pin blanks to boards by compressivedeformation. Part of pin blank receiving hole 34 in lower hammer 36defines its own bulge cavity 42 having a shape similar to bulge cavity38 in upper hammer 40. As used herein, "upper" and "lower" refer to theposition as shown in the FIG. 1, but physically they can be reversed oreven spaced laterally or other direction rather than vertically.

With the elements arranged in this manner, lower hammer 36 and upperhammer 40 are moved together in the axial direction, i.e., in thedirection of the longitudinal axis of pin blank 14. This causes thefirst end 24 of the pin blank to be inserted into hole 16 of board 12and then for the pin blank to be moved all the way into hole 16 untilsubstrate-engaging section 28 of the pin blank aligns with the body ofthe board and the end 24 of the pin protrudes out of hole 16 just pastpads 23 of electrically conductive material 22. At the same time,movement of the hammers together also causes end 26 and compliantsection 30 of pin 14 to be received in pin blank receiving hole 34 oflower hammer 36.

Movement of lower hammer 36 and upper hammer 40 together is continueduntil they reach a predetermined distance apart, this distance being, inthe particular embodiment shown, the thickness of electrical substrate12 including pads 23 of electrically conductive material 22. As will beappreciated by those skilled in the art, movement of the upper and lowerhammers together in this manner causes a compressive force to be exertedupon the body of pin blank 14 along its longitudinal axis. Thiscompressive force in turn causes a compressive deformation, i.e.,plastic deformation, of those portions of the substrate-engaging section28 of the pin blank immediately below and above the first and secondsurfaces, respectively, of printed circuit board 12. This plasticdeformation, in turn, causes bulges 44 and 46 to form in the body of thepin blank, these bulges being formed by the material of pin blank 14filling bulge cavities 38 and 42 of upper and lower hammers 40 and 36,respectively. As well known to those skilled in the art, bulges 44 and46 act to sandwich or hold board 12 therebetween, thereby firmly andsecurely affixing the pin blank to the board, pin blank 14 now beingreferred to simply as a pin. Lower hammer 36 and upper hammer 40 arethen moved to a retracted position, thereby producing a completed module10 in accordance with the present invention.

Although FIGS. 1 and 2 illustrate only a single pin blank being affixedto printed circuit board 12, in actual practice there will normally bemultiple pin blanks affixed to multiple holes in the substrate. By thistechnique, a module is provided which, as illustrated in FIG. 3, definesa plurality, or array, of pins 14, each having a compliant sectionprojecting from the first surface 18 of the board for subsequentconnection of module 10 to another printed circuit board or other deviceby compliant pin connection, as more fully described below.

FIGS. 4, 5 and 6 illustrate how the inventive module 10 prepared asdescribed above can be connected to another circuit board or otherdevice (known in the art by various terms such as "carrier," "motherboard," "planar," etc.) for forming a completed assembly of stackedboards or devices. Referring to FIG. 4, module 10 is arranged so thatsecond end 26 of pin 14 registers with opening 48 in a second electricalsubstrate 50, which in the embodiment shown is also a printed circuitboard. Opening 48 in printed circuit board 50 has a size compatible withcompliant section 30 of pin 14 so that when this section is insertedinto opening 48, protrusions 32 in the compliant section 30 firmly affixpin 14 to circuit board 50 by compliant pin connection. In theparticular embodiment shown, the walls of opening 48 in board 50 areplated through holes provided with a coating 52 of an electricallyconductive material for providing electrical connection to pin 14 aswell as mechanical connection. Printed circuit board 50 also includes anelectrically conductive path (not shown) connected to the electricallyconductive material 52 in hole 48 for electrical connection of pin 14 toother elements on printed circuit board 50.

With pin 14 arranged in registration with hole 48 of printed circuit 50,module 10 and circuit board 50 are brought together to insert pin 14into hole 48 of the circuit board. This operation is accomplished in theembodiment shown by means of a press 54 and a mounting plate 56. Press54 includes projections 58 for engaging the bulge 46 of pin 14, whilemounting plate 56 defines holes 60 for receiving the portion of the bodyof pin 14 extending out of the bottom of the second printed circuit whenmodule 10 and board 50 are brought together for their final positioning.

As illustrated in FIG. 5, mounting plate 56 and press 54 are broughttogether until stopped by a suitable stop 62 which is so arranged thatconverging movement of the press and mounting plate is stopped whenprotrusions 32 of pin 14 align with the axial center of hole 48. As willbe appreciated by those skilled in the art, suitable spacer elements(not shown) may also be provided to insure that module 10 and board 50remain spaced apart by a predetermined distance as press 54 and mountingplate 56 are moved together. In any event, insertion of compliantsection 30 of pin 14 into hole 48 and convergence of press 54 andmounting plate 56 in the manner described above causes compliant section30 of pin 14 and the walls of hole 48 to be firmly affixed together,thereby creating a secure mechanical and electrical bond in accordancewith known compliant pin connection techniques. Press 54 and mountingplate 56 are then withdrawn from one another to form a completedassembly 64 as illustrated in FIG. 6.

As shown in FIG. 6, completed assembly 64 comprises a first circuitboard 12 and second circuit board 50 which are securely affixed to oneanother, both mechanically and electrically by means of pin 14. Inactual practice, many pins will normally be employed rather than thesingle pin illustrated in the figure so that numerous electrical andmechanical connections can be made, thereby making the connectionbetween boards 12 and 50 even more secure.

From the foregoing, it can be seen that the present invention provides asimple and straightforward method for mechanically and electricallyforming together multiple circuit boards in stacked relation withoutsoldering. In particular, it can be seen that the procedure of theinvention requires only simple movement of suitable anvils, hammers andother work pieces in the longitudinal direction, that is the directionaligning with the longitudinal axis of the pin blanks. Moreover, it canalso be seen that the pin blanks used in the present invention are ofsimple design, not requiring involved mechanical steps to developcomplex shapes or structures as in prior art systems. These featuresmake the inventive technique for joining multiple circuit boardstogether inexpensive to carry out while at the same time providingsecure electrical connections throughout the completed device.

In accordance with another feature of the invention, a novel hammer oranvil is provided for inserting pin blank 14 into the substrate orcircuit board 12 illustrated above. In this connection, an importantfeature of lower hammer 36 is that pin blank receiving hole 34 is sizedand shaped to receive the lower end of pin 14 therein, even though thisportion of pin 14 includes a compliant pin section 30. The structure tomake this possible is more fully illustrated in FIG. 7. As shown in thisfigure, pin blank receiving hole 34 in lower hammer 36, in addition toincluding bulge cavity 42 as previously described, includes two grooves66 axially arranged in the walls of pin blank receiving hole 34 toreceive protrusions 32 of pin blank 14. As shown in FIG. 2, thesegrooves 66 extend downwardly by a distance sufficient to accommodateprotrusions 32 when pin 14 is inserted in lower hammer 36 by sufficientdistance so that the bottom 68 of pin engaging hole 34 engages the end26 of the pin. By this means, lower hammer 36 can be used together withupper hammer 40 to cause compressive deformation of pin blank 14 therebyforming bulges 44 and 46 in the manner described above.

In accordance with another feature of the invention, a third electricalsubstrate or printed circuit board can be stacked with the assembly oftwo printed circuit boards shown in FIG. 6. In accordance with thisembodiment of the invention, a pin is used which has two compliantsections, one near each of the two ends of the pin blank with thesubstrate-engaging section being located therebetween. In thisembodiment, it is preferable that the diameter of the substrate-engagingsection be larger than the diameter of the pin in the other sections,and preferably at least as large as the largest cross-sectionaldimension of the pin at the protrusions 32. With this configuration, apreformed pin can still be inserted into the hole 16 of board 12 andthen moved therethrough until the substrate-engaging section 28 of thepin aligns with board 12. In this configuration, the pin blank is againsubjected to compression along its longitudinal axis, but in thisembodiment upper hammer 40 is provided with a pin blank receiving holehaving essentially the same structure as pin blank receiving hole 34 inlower hammer 36. As a result, upper hammer 40 can receive the ends ofthe pins projecting from the upper surface 20 of board 12 in the sameway lower hammer 36 receives the ends of the pins projecting downwardlyfrom lower surface 18 of the board.

When this embodiment of the invention is employed, there is produced amodule as illustrated in FIG. 8, the pins of such module projecting afirst array of compliant sections 30 downward from the first surface 18of the substrate and a second array of compliant sections upward fromthe second surface 20 of the substrate. Each of these arrays ofcompliant sections can be firmly affixed to its own printed circuit orother device by compliant pin connection, thereby creating a 3-layeredstacked assembly as desired. This is illustrated in FIG. 9.

The present invention can be employed to form printed circuit boards,modules, module assemblies and other devices of any size. Typicalcircuit boards used today measure 25×25 to 75×75 millimeters and containan array of 5 to 500 pin/holes, for example. Conventional pin sizesinclude pins of 16, 18, 20, etc., mils in diameter with the individualpins being spaced apart by any suitable distance, for example 1.27 to2.54 millimeters. The invention described herein is applicable toprinted circuit boards and other electrical devices of any such sizes.In addition, the present invention is also applicable to the productionof printed circuit boards and other electrical devices of even largerconstruction, with the assemblies once formed being subdivided intosmaller subassemblies after formation.

Although only a few embodiments of the present invention have beendescribed above, it should be appreciated that many modifications can bemade without departing from the spirit and scope of the invention. Forexample, although lower hammer 36 has been described as being a single,unitary member, it should be appreciated that lower hammer 36 can becomposed of a number of different pieces or devices so long as theoverall function of the hammer remains the same. For example, hammer 36could be divided into two or more pieces, one or more pieces arranged toaccept and hold the compliant portion 30 of pin blank 14 and anotherdevice employed for the application of axial force to end 26 of the pinblank.

Furthermore, although the foregoing has described the holes and openingsin the first and second circuit boards as including contacts allowingelectrical connection of the pins thereto, it should be appreciated thatelectrical connections are not always necessary, mechanical connectionsonly being sufficient for some applications.

Furthermore, although the foregoing description indicates that theelectrically conductive material 22 in openings 16 form pads 23 on thefirst and second surfaces of the substrate, it should be appreciatedthat such pads are not required. In the same way, using pins and pinblanks of circular cross-section is not required, as any cross-sectionalshape can be employed. Also, the diameter of the pin blanks used inaccordance with the present invention can vary from section to sectionas desired, it being sufficient in accordance with the present inventionmerely that hole 34 in hammer 36 (whether formed from single or multiplepieces) receive and accommodate so much of compliant section 30 of thepin as is necessary to accomplish compressive deformation of the pinblank as described above.

In addition, although the foregoing shows using pin blanks withpre-formed compliant sections, it should be appreciated that the pinblanks can be affixed to substrate 12 before the pin blank is swaged orotherwise worked to form compliant sections. This, of course, defeatsone of the major advantages of the present invention in using preformedpin blanks for the sake of ease of operation and low cost.

All such modifications are intended to be included within the scope ofthe present invention, which is to be limited only by the followingclaims.

We claim:
 1. A hammer for forming bulges in an array of compliant pinblanks by compressive deformation to thereby attach said array of pinblanks to a printed circuit board, each of said compliant pin blankshaving a substrate-engaging portion and a compliant section spaced fromsaid substrate-engaging portion and projecting from said printed circuitboard when said pin blank is inserted therein, the compliant section ofeach of said pin blanks defining at least one protrusion extendingoutwardly from the central axis of the pin blank farther than theremaining portions of the compliant section of the pin blank, saidprinted circuit board having a plurality of holes receiving thesubstrate-engaging portions of said array of compliant pin blanks,saidhammer comprising a body defining a substrate-facing surface for facingsaid printed circuit board when said compliant pin blanks are attachedthereto, said body defining a plurality of holes in saidsubstrate-facing surface for receiving the compliant sections of saidpin blanks, each of said holes being elongated and arranged generallyperpendicular to said substrate-facing surface, each of said holesdefining in said substrate-facing surface a bulge cavity larger incross-section than the cross-section of the portion of pin blankreceived therein so that compressive stress of said pin blanks willcause said blanks to deform and thereby form bulges in the bulgecavities, each of said holes further defining at least one groovetherein, one groove corresponding to each of the protrusions in therespective compliant sections of said pins, each of said at least onegroove in each of said holes being shaped to receive its respectiveprotrusion when said array of pins is placed in said holes.
 2. Thehammer of claim 1 wherein said protrusions are formed by swaging andfurther wherein said at least one groove extends axially along the wallsof said holes.